In the packaging field, the application of liquid adhesives to packaging materials is sometimes carried out by extruding the adhesives onto the packaging materials through orifices in a contact extrusion head. Such heads are commonly connected to a reservoir of the liquid under pressure, and a control valve is connected between the reservoir and the head. A problem with that type of system has been the tendency of the adhesive to set up in the orifices when the control valve is closed to interrupt liquid flow through the head. One attempt to alleviate that problem utilized self closing nipple-like check valve members at each orifice. These valves were intended to automatically seal the interior of the head from the ambient when liquid flow through the head terminated. Such attempts have not been entirely successful inasmuch as they do not completely eliminate the dripping or plugging of the orifices after liquid flow to the head is terminated. Consequently, the extrusion heads which are now in use require frequent cleaning and unplugging of the orifices. More importantly, however, unless closely watched during use, one or more of the orifices become plugged so that an improper pattern is placed on the material to be glued. When such plugging is discovered it is necessary to shut down the line to clean or replace the plugged head unless backup heads are provided.